Methods of fabricating semiconductor devices having conductive pad structures with multi-barrier films

ABSTRACT

Methods of fabricating semiconductor devices are provided. The method includes providing a substrate and forming an interconnect structure on the substrate. The interconnect structure includes a top metal layer. The method also includes forming a first barrier film on the top metal layer using a first deposition process with a first level of power, and forming a second barrier film on the first barrier film using a second deposition process with a second level of power that is lower than the first level of power. The method further includes forming an aluminum-containing layer on the second barrier film. In addition, the method includes patterning the first barrier film, the second barrier film and the aluminum-containing layer to form a conductive pad structure.

PRIORITY CLAIM AND CROSS-REFERENCE

This application claims the benefit of U.S. Provisional Application No.62/711,903, filed on Jul. 30, 2018, the entirety of which isincorporated by reference herein.

BACKGROUND

Semiconductor devices are used in a variety of electronic applications,such as personal computers, cell phones, digital cameras, and otherelectronic equipment. Semiconductor devices are typically fabricated bysequentially depositing insulating or dielectric layers, conductivelayers, and semiconductor layers of material over a semiconductorsubstrate, and patterning the various material layers using lithographyto form circuit components and elements on the semiconductor substrate.

Once the fabrication of a semiconductor device is complete, a bondingpad formed on the fabricated semiconductor device is coupled to anexternal electronic element using one of various bonding processes. Onecommon bonding process is performed by forming a bonding wire or asolder ball on the bonding pad to connect the external electronicelement with the bonding pad. Although existing bonding pads have beengenerally adequate for their intended purposes, they have not beenentirely satisfactory in all respects.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It shouldbe noted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 shows a cross-sectional view of a semiconductor device having aconductive pad structure, in accordance with some embodiments.

FIG. 2 is a flow chart of an exemplary method of forming a conductivepad structure of a semiconductor device, in accordance with someembodiments.

FIGS. 3A-3E show cross-sectional views of respective intermediatestructures for forming a conductive pad structure, in accordance withsome embodiments.

FIG. 4 shows a cross-sectional view of a semiconductor device having aconductive pad structure, in accordance with some embodiments.

FIGS. 5A-5G show cross-sectional views of respective intermediatestructures for forming a conductive pad structure and forming aconductive bump on the conductive pad structure, in accordance with someembodiments.

FIG. 6 shows a cross-sectional view of a semiconductor device having aconductive pad structure and a conductive connection feature on theconductive pad structure, in accordance with some embodiments.

FIG. 7 shows a cross-sectional view of a semiconductor image sensordevice having a conductive pad structure, in accordance with someembodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of electronic elements and arrangements aredescribed below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Forexample, the formation of a first feature over or on a second feature inthe description that follows may include embodiments in which the firstand second features are formed in direct contact, and may also includeembodiments in which additional features may be formed between the firstand second features, such that the first and second features may not bein direct contact. In addition, the present disclosure may repeatreference numerals and/or letters in the various examples. Thisrepetition is for the purpose of simplicity and clarity and does not initself dictate a relationship between the various embodiments and/orconfigurations discussed.

Some variations of the embodiments are described. Throughout the variousviews and illustrative embodiments, like reference numbers are used todesignate like elements. It should be understood that additionaloperations can be provided before, during, and after the method, andsome of the operations described therein can be replaced or eliminatedfor other embodiments of the method.

Embodiments disclosed herein relate generally to fabricatingsemiconductor devices having a conductive pad structure withmulti-barrier films to prevent metal extrusion. The metal extrusion isfrom a metal layer under the conductive pad structure and/or from analuminum-containing layer of the conductive pad structure. In someembodiments, the metal layer under the conductive pad structure is a topmetal layer of an interconnect structure. The top metal layer maycontain copper (Cu).

According to embodiments of the disclosure, the multi-barrier films ofthe conductive pad structure can prevent copper (Cu) of the top metallayer from extrusion. In addition, the multi-barrier films of theconductive pad structure can prevent aluminum (Al) of thealuminum-containing layer of the conductive pad structure fromextrusion. The metal extrusions will cause adjacent pads ofsemiconductor devices occurring a short circuit. The embodiments of thedisclosure can overcome the metal extrusions, and the production yieldand the reliability of the semiconductor devices are thereby enhanced.

In some embodiments, the multi-barrier films of the conductive padstructure include a first barrier film and a second barrier film. Thesecond barrier film is disposed between the first barrier film and thealuminum-containing layer of the conductive pad structure. The firstbarrier film is formed on a top metal layer of an interconnect structureusing a first deposition process with a first level of power. The secondbarrier film is formed on the first barrier film using a seconddeposition process with a second level of power. The second level ofpower used for depositing the second barrier film is lower than thefirst level of power used for depositing the first barrier film.

According to embodiments of the disclosure, the second barrier filmformed using a lower level of power has an amorphous structure toprovide a metal barrier ability for the metal of the top metal layerunder the second barrier film. Moreover, the second barrier film formedusing a lower level of power has a high compressive stress to balancewith the tensile stress of the aluminum-containing layer above thesecond barrier film. Therefore, the multi-barrier films of theconductive pad structure can prevent the metal extrusion of the topmetal layer of the interconnect structure and the metal extrusion of thealuminum-containing layer of the conductive pad structure.

The foregoing broadly outlines some aspects of embodiments. Someembodiments described herein are described in the context of aconductive pad structure of semiconductor devices and methods forforming the conductive pad structure. The semiconductor devices may beany type semiconductor devices having contact pads and/or bonding padsfor electrical connection. The semiconductor devices are for example,Fin Field Effect Transistor (FinFET) devices, semiconductor image sensordevices, or other semiconductor devices. In addition, the conductive padstructures of the embodiments of the disclosure may be applied tothree-dimensional (3D) packages for bonding stacked dies, chips,fabricated wafers, or interposer substrates. Some variations of theexemplary methods and structures are described. A person having ordinaryskill in the art will readily understand other modifications may be madethat are contemplated within the scope of other embodiments. Althoughembodiments of the method may be described in a particular order,various other embodiments of the method may be performed in any logicalorder and may include fewer or more operations than what is describedherein.

Embodiments for forming semiconductor devices having conductive pads areprovided. FIG. 1 shows a cross-sectional view of a semiconductor device100 having a conductive pad structure 120, in accordance with someembodiments. A substrate 102 is provided, as shown in FIG. 1 inaccordance with some embodiments. The substrate 102 may be a bulksemiconductor substrate, a semiconductor-on-insulator (SOI) substrate,or other semiconductor substrate, which may be doped (e.g., with ap-type or an n-type dopant) or undoped. Generally, an SOI substrateincludes a layer of a semiconductor material formed on an insulatorlayer. The insulator layer may be, for example, a buried oxide (BOX)layer, a silicon oxide layer, or other insulating material. Theinsulator layer is provided on a silicon or glass substrate. Thesubstrate 102 may be made of silicon or other semiconductor material.For example, the substrate 102 is a silicon wafer. In some examples, thesubstrate 102 is made of a compound semiconductor such as siliconcarbide, gallium arsenic, indium arsenide, or indium phosphide. In someexamples, the substrate 102 is made of an alloy semiconductor such asGaAsP, AlInAs, AlGaAs, GaInAs, GaInP, or GaInAsP.

The substrate 102 may comprise multiple electronic elements 104 formedtherein or thereon. The electronic elements 104 may be active electronicelements such as P-channel field-effect transistors (PFETs), N-channelFETs (NFETs), metal-oxide-semiconductor field-effect transistors(MOSFETs), complementary metal-oxide-semiconductor (CMOS) transistors,bipolar transistors, high voltage transistors, high frequencytransistors, memory cells, and/or a combination thereof. Furthermore,the electronic elements 104 may be passive electronic elements such asresistors, capacitors, and inductors. The substrate 102 may furthercomprise static random access memory (SRAM) and/or other logic circuitsformed therein or thereon.

An interconnect structure 110 is formed over the substrate 102 forelectrically coupling various electronic elements 104 to fabricateintegrated circuit. In the illustrated embodiment of FIG. 1, there arethree metal layers 106 and a top metal layer 106T in the interconnectstructure 110, but other numbers of metal layers may be used in otherembodiments. For example, the interconnect structure 110 may includefive to ten metal layers, but fewer or more metal layers are used inother embodiments. The multiple metal layers of the interconnectstructure 110 include the top metal layer 106T and the other metallayers 106. The metal layers 106 and the top metal layer 106T aredisposed in multiple inter-metal-dielectric (IMD) layers 107 of theinterconnect structure 110. The interconnect structure 110 also includesmultiple vias 108 disposed in the IMD layers 107 between the metallayers 106 and the top metal layer 106T for providing a verticalelectrical connection between the adjacent metal layers. The metallayers 106 and the top metal layer 106T can provide a horizontalelectrical connection for the interconnect structure 110.

In some embodiments, the metal layers 106 and the top metal layer 106Tare made of the same material, such as selected from a group consistingof aluminum, aluminum silicon, copper, other metals and various alloys.In some other embodiments, the metal layers 106 and the top metal layer106T are made of different materials, such as selected from a groupconsisting of aluminum, aluminum silicon, copper, other metals andvarious alloys. In one embodiment, the top metal layer 106T and themetal layers 106 are all made of copper. In some embodiments, the vias108 are made of various suitable conductive materials, such as but notlimited to aluminum, aluminum silicon, copper, aluminum copper, othermetal or alloy. In some examples, the vias 108 include barrier typematerials such as tungsten as a liner of the vias 108.

In some embodiments, the inter-metal-dielectric (IMD) layers 107 aremade of various suitable dielectric materials, such as silicon oxide,silicon nitride, silicon oxynitride, high dielectric constant (high-k)dielectric materials, or another suitable dielectric material. In someexamples, the multiple IMD layers 107 are made of the same dielectricmaterial. In some other examples, the multiple IMD layers 107 are madeof different dielectric materials. In some embodiments, the metal layers106, the top metal layer 106T, and the vias 108 are formed using adamascene process or a dual damascene process. In the dual damasceneprocess, a via opening and a trench opening are formed in the IMD layers107 using two etching processes, in which the trench opening is abovethe via opening. The via opening and the trench opening are filled witha conductive material. Then, the conductive material outside of thetrench opening is removed by a planarization process such as a chemicalmechanical polishing (CMP) process to form the metal layer 106 or thetop metal layer 106T in the trench opening and to form the via 108 inthe via opening.

Multiple conductive pad structures 120 are formed on the top metal layer106T of the interconnect structure 110, as shown in FIG. 1 in accordancewith some embodiments. The conductive pad structures 120 are in contactwith the top metal layer 106T. If the metal of the top metal layer isextruded from the top metal layer into the space between adjacent padsafter the semiconductor device is subjected to a thermal process, therewill be a short circuit between the adjacent pads. According to someembodiments of the disclosure, the conductive pad structure 120 includesa first barrier film 122 on the top metal layer 106T, a second barrierfilm 124 on the first barrier film 122, and an aluminum-containing layer126 on the second barrier film 124. The configuration of the firstbarrier film 122 and the second barrier film 124 can avoid the metalextrusion of the top metal layer 106T. Therefore, there is no shortcircuit occurring between the adjacent conductive pad structures 120.The more details will be described as following.

FIG. 2 is a flow chart of an exemplary method 200 of forming aconductive pad structure of a semiconductor device, for example theconductive pad structure 120 of the semiconductor device 100 of FIG. 1,in accordance with some embodiments. FIGS. 3A-3E show cross-sectionalviews of respective intermediate structures for forming a conductive padstructure, for example the conductive pad structure 120 of thesemiconductor device 100 of FIG. 1, in accordance with some embodiments.The method 200 as shown in FIG. 2 may be described with reference toFIG. 1 and FIGS. 3A-3E.

In operation 202 of the method 200, an interconnect structure is formedon a substrate. The interconnect structure includes a top metal layer.For example, the interconnect structure 110 is formed on the substrate102, as shown in FIG. 1 in accordance with some embodiments. Theinterconnect structure 110 includes the top metal layer 106T. Thedetails of the interconnect structure 110 are described in theabove-mentioned description and are not repeated again.

In operation 204 of the method 200, a first barrier film is deposited onthe top metal layer using a first deposition process with a first levelof power. For example, the first barrier film 122 is formed on the topmetal layer 106T using the first deposition process with the first levelof power, as shown in FIG. 3A in accordance with some embodiments. Insome embodiments, the first barrier film 122 is made of metal nitridesuch as a tantalum nitride (TaN) film. The first deposition processincludes a physical vapor deposition (PVD) process, sputtering,evaporation, atomic layer deposition (ALD) process or another suitabledeposition process. The first level of power used in the firstdeposition process such as a PVD process is for example to produce Argon(Ar) plasma. In some embodiments, the first level of power is in a rangefrom about 2000 W to about 10000 W, for example about 6000 W. In someother embodiments, the first barrier film 122 may be made of othersuitable barrier materials to prevent the metal of the top metal layer106T from extrusion. In some embodiments, the first barrier film 122 hasa thickness T1 in a range from about 400 Å to about 800 Å, for examplefrom about 484 Å to about 684 Å.

In operation 206 of the method 200, a second barrier film is depositedon the first barrier film using a second deposition process with asecond level of power that is lower than the first level of power. Forexample, the second barrier film 124 is formed on the first barrier film122 using the second deposition process with the second level of power,as shown in FIG. 3B in accordance with some embodiments. In someembodiments, the second barrier film 124 is made of the same material asthe first barrier film 122. For example, the second barrier film 124 mayalso be a tantalum nitride (TaN) film. The second deposition processincludes a physical vapor deposition (PVD) process, sputtering,evaporation, atomic layer deposition (ALD) process or another suitabledeposition process. The second level of power used in the seconddeposition process such as a PVD process is for example to produce Arplasma. In some embodiments, the second level of power in a range fromabout 100 W to lower than about 2000 W, for example about 500 W. In someother embodiments, the second barrier film 124 may be made of othersuitable barrier materials to prevent the metal of the top metal layer106T from extrusion. In some embodiments, the second barrier film 124has a thickness T2 in a range from about 5 Å bout 200 Å, for examplefrom about 10 Å to about 180 Å. In some embodiments, the thickness T1 ofthe first barrier film 122 is in a range from about 2.5 times to about70 times greater than the thickness T2 of the second barrier film 124.

In operation 208 of the method 200, an aluminum-containing layer isformed on the second barrier film. For example, the aluminum-containinglayer 126 is formed on the second barrier film 124, as shown in FIG. 3Cin accordance with some embodiments. In some embodiments, thealuminum-containing layer 126 may be an aluminum copper alloy (AlCu)layer, an aluminum (Al) layer or made of other conductive materialcontaining aluminum and providing a satisfactory conductivity. Thealuminum-containing layer 126 may be formed using a physical vapordeposition (PVD) process, sputtering, evaporation, atomic layerdeposition (ALD) process or another suitable deposition process. In someexamples, the aluminum-containing layer 126 has a thickness in a rangefrom about 500 Å to about 1000 Å.

In operation 210 of the method 200, the aluminum-containing layer, thefirst barrier film and the second barrier film are patterned to form aconductive pad structure. For example, the aluminum-containing layer126, the first barrier film 122 and the second barrier film 124 arepatterned to form the conductive pad structure 120, as shown in FIGS. 3Dand 3E in accordance with some embodiments. In some embodiments, anetching mask 128 is formed on the aluminum-containing layer 126 as shownin FIG. 3D. The etching mask 128 may be a patterned photoresist layer ora hard mask. The patterned photoresist layer can be formed using aphotolithography technology. The photolithography technology includesforming a photoresist layer overlying the aluminum-containing layer 126,exposing the photoresist layer to a pattern through a photo-mask,performing a post-exposure bake process, and developing the photoresistlayer to pattern the photoresist layer to form the patterned photoresistlayer as the etching mask 128.

In some other examples, the etching mask 128 is a hard mask that can beformed using photolithography and etching processes. First, a mask layer(not shown) is formed on the aluminum-containing layer 126. Next, aphotoresist layer (not shown) is formed overlying the mask layer. Thephotoresist layer is patterned using a photolithography technology thatincludes exposing the photoresist layer to a pattern through aphoto-mask, performing a post-exposure bake process, and developing thephotoresist layer to pattern the photoresist layer. Thereafter, thepattern of the photoresist layer is transferred to the mask layer usinga suitable etching process to form the hard mask as the etching mask128.

The aluminum-containing layer 126, the first barrier film 122 and thesecond barrier film 124 are patterned using a suitable etching processwith the etching mask 128 to protect the portions of thealuminum-containing layer 126, the first barrier film 122 and the secondbarrier film 124 under the etching mask 128. The etching process may beone or more etching steps which are selected to the materials of thealuminum-containing layer 126, the first barrier film 122 and the secondbarrier film 124. As a result, the conductive pad structure 120 isformed on the top metal layer 106T, as shown in FIG. 3E in accordancewith some embodiments.

In some embodiments of the disclosure, both the first barrier film 122and the second barrier film 124 are tantalum nitride (TaN) films. Thesecond barrier film 124 is deposited using a lower level of power thanthat for depositing the first barrier film 122. Therefore, the secondbarrier film 124 has a higher nitrogen (N) atomic percentage than thatof the first barrier film 122. In some embodiments, the N atomicpercentage of the second barrier film 124 is in a range from about 2.5times to about 5 times greater than the N atomic percentage of the firstbarrier film 122. In some embodiments, the second barrier film 124 hasan atomic ratio of N to TaN in a range from about 0.86 to about 0.93.The first barrier film 122 has an atomic ratio of N to TaN in a rangefrom about 0.19 to about 0.31. In some embodiments, the N to TaN atomicratio of the second barrier film 124 to the N to TaN atomic ratio of thefirst barrier film 122 is in a range from about 2.5 to about 5.0, forexample about 2.77 to about 4.90.

A tantalum nitride (TaN) film with a higher N to TaN atomic ratio has anamorphous structure while another TaN film with a lower N to TaN atomicratio has a crystalline structure. The TaN film with an amorphousstructure has a metal (for example Cu) barrier ability better than thatof the TaN film with a crystalline structure. Therefore, the secondbarrier film 124 having a higher N to TaN atomic ratio can provide abetter metal barrier ability than that of the first barrier film 122having a lower N to TaN atomic ratio. According to the embodiments ofthe disclosure, the second barrier film 124 deposited using a low levelof power can provide a better metal barrier ability to prevent the metalsuch as Cu of the top metal layer 106T from extrusion. As the N to TaNatomic ratio of the second barrier film 124 is higher, the amount ofmetal (such as Cu) extrusion of the top metal layer 106T is lower.

In addition, the aluminum-containing layer 126 such as AlCu layer has atensile stress. The tensile stress of the aluminum-containing layer 126cause Al extrusion that will damage the conductive pad structure 120. Atantalum nitride (TaN) film with a higher N to TaN atomic ratio has ahigher compressive stress than another TaN film with a lower N to TaNatomic ratio. Therefore, the second barrier film 124 with a higher N toTaN atomic ratio has a higher compressive stress than that of the firstbarrier film 122 to balance the tensile stress of thealuminum-containing layer 126. As the tensile stress of thealuminum-containing layer 126 is lower, the amount of Al extrusion ofthe aluminum-containing layer 126 is lower.

According to the embodiments of the disclosure, the second barrier film124 deposited using a low level of power can provide a high compressivestress to balance the tensile stress of the aluminum-containing layer126 and thereby prevent Al extrusion of the aluminum-containing layer126. As a result, conductive pad structures 120 of good quality areobtained to improve the yield of semiconductor devices.

In some examples, the second barrier film 124 is replaced with a Tafilm. The Ta film has a crystalline structure, and thereby has low metalbarrier ability. The metal (such as Cu) of the top metal layer 106T caneasily pass through the crystalline structure of the Ta film and causeCu extrusion defect around the conductive pad structure. According tothe embodiments of the disclosure, the second barrier film 124 such asTaN film deposited using a low level of power has an amorphousstructure, and thereby has a better metal barrier ability than the Tafilm to prevent Cu extrusion of the top metal layer 106T.

In addition, the Ta film has a lower compressive stress than the secondbarrier film 124 such as TaN film deposited using a low level of power.While compared with the second barrier film 124 of the embodiments, thelower compressive stress of the Ta film has a poor effect to balance thetensile stress of the aluminum-containing layer 126. After a subsequentthermal process is performed on the aluminum-containing layer 126, forexample a process temperature of about 400° C., a conductive padstructure with the Ta film disposed under the aluminum-containing layeris easy to cause Al extrusion defect. In order to avoid the Alextrusion, the equipment for the Ta film deposition needs to beconfigured with an additional chiller to reduce the temperature of theprocess chamber, and the fabrication cost is thereby increased.Moreover, an extra cooling time is added in queue time (Q-time) of waferto wafer, and the fabrication yield is thereby decreased. According tothe embodiments of the disclosure, the above-mentioned problems can beovercome.

FIG. 4 shows a cross-sectional view of a semiconductor device 300 havinga conductive pad structure 120, in accordance with some embodiments. Thedifference between the semiconductor device 300 of FIG. 4 and thesemiconductor device 100 of FIG. 1 is that a passivation layer 127 isformed on the top metal layer 106T of the interconnect structure 110.The passivation layer 127 has an opening to expose a portion of the topmetal layer 106T. The conductive pad structure 120 is formed in theopening of the passivation layer 127 and onto a partial top surface ofthe passivation layer 127, as shown in FIG. 4 in accordance with someembodiments.

Moreover, the aluminum-containing layer 126, the first barrier film 122and the second barrier film 124 of the conductive pad structure 120 areconformally deposited in the opening of the passivation layer 127 andonto the partial top surface of the passivation layer 127 to produce arecess of the conductive pad structure 120. The recess of the conductivepad structure 120 may help a conductive connection feature (not shown)such as a bonding wire or a solder ball to be bonded with the conductivepad structure 120. The conductive connection feature is provided forelectrically coupling the conductive pad structure 120 to an externalcircuit.

The semiconductor device 300 includes a substrate 102, as shown in FIG.4 in accordance with some embodiments. The substrate 102 may be a bulksemiconductor substrate, a semiconductor-on-insulator (SOI) substrate,or other semiconductor substrate, which may be doped (e.g., with ap-type or an n-type dopant) or undoped. The substrate 102 may be made ofsilicon or other semiconductor material. In some examples, the substrate102 is made of a compound semiconductor such as silicon carbide, galliumarsenic, indium arsenide, or indium phosphide. In some examples, thesubstrate 102 is made of an alloy semiconductor such as GaAsP, AlInAs,AlGaAs, GaInAs, GaInP, or GaInAsP.

Multiple electronic elements 104 are formed in or on the substrate 102.The electronic elements 104 include static random access memory (SRAM)cells, active electronic elements, passive electronic elements and/orother logic circuits. The active electronic elements are for exampleP-channel field-effect transistors (PFETs), N-channel FETs (NFETs),metal-oxide-semiconductor field-effect transistors (MOSFETs),complementary metal-oxide-semiconductor (CMOS) transistors, bipolartransistors, high voltage transistors, high frequency transistors, othermemory cells, and/or a combination thereof. The passive electronicelements are for example resistors, capacitors, and inductors.

The interconnect structure 110 is formed over the substrate 102 forelectrically coupling various electronic elements 104 to fabricateintegrated circuit. The interconnect structure 110 includes multiplemetal layers 106, a top metal layer 106T, and multiple vias 108 ininter-metal dielectric (IMD) layers 107. The vias 108 provide verticalconnection for electrically coupling the adjacent metal layers 106 andthe top metal layer 106T. The materials and processes for forming themetal layers 106, the top metal layer 106T, the vias 108, and the IMDlayers 107 may be the same as or similar to those described with respectto FIG. 1, and not repeated again.

The passivation layer 127 is formed over the interconnect structure 110,as shown in FIG. 4 in accordance with some embodiments. The passivationlayer 127 has an opening to expose a portion of the top metal layer 106Tfor subsequently forming the conductive pad structure 120 in contactwith the exposed portion of the top metal layer 106T. The passivationlayer 127 further covers other portion of the top metal layer 106T forprotecting the interconnect structure 110. Thereafter, the first barrierfilm 122, the second barrier film 124 and the aluminum-containing layer126 are sequentially deposited in the opening of the passivation layer127 and on the surface of the passivation layer 127 to form theconductive pad structure 120, as shown in FIG. 4 in accordance with someembodiments.

In some examples, the passivation layer 127 is made of an organicinsulating material such as polyimide, epoxy resin or another suitableinsulating material. In some other examples, the passivation layer 127is made of an inorganic insulating material such as silicon oxide,silicon nitride, silicon oxynitride or other low dielectric constant(low-k) dielectric material. The passivation layer 127 can be patternedusing photolithography and etching processes to form the opening.

In some embodiments, the first barrier film 122, the second barrier film124 and the aluminum-containing layer 126 may be deposited using theprocesses and the materials which are the same as or similar to thoseused for the corresponding components of the conductive pad structure120 in FIG. 1. Also, the first barrier film 122, the second barrier film124 and the aluminum-containing layer 126 may be deposited using theprocesses and the materials with respect to the descriptions of themethod 200 in FIG. 2 and the cross-sectional views of respectiveintermediate structures for forming the conductive pad structure 120 inFIGS. 3A-3E.

FIGS. 5A-5G show cross-sectional views of respective intermediatestructures for forming the conductive pad structure 120 of FIG. 4 andforming a conductive bump 134 on the conductive pad structure 120, inaccordance with some embodiments. A passivation material layer (notshown) is formed on the top metal layer 106T. In some examples, thepassivation material layer may be polyimide, epoxy resin or otherorganic insulating material, which are photosensitive materials. Thepassivation material layer may be formed on the top metal layer 106Tusing a coating process. The passivation material layer is exposed tolight through a photomask. Then, the passivation material layer ispatterned using a development process to remove the exposed or unexposedportion of the passivation material layer to form the passivation layer127 with an opening 129 therein, as shown in FIG. 5A in accordance withsome embodiments. The exposed or unexposed portion of the passivationmaterial layer is removed by the development process depending on thatthe passivation material layer is positive or negative type photoresist.

In some other examples, the passivation material layer may be siliconoxide, silicon nitride, silicon oxynitride or other low-k dielectricmaterial. A patterned photoresist (not shown) is formed on thepassivation material layer through a photolithography process such asthe above-mentioned description. Thereafter, the passivation materiallayer is etched through using the patterned photoresist as an etchingmask to form the passivation layer 127 with an opening 129 therein, asshown in FIG. 5A in accordance with some embodiments. The etchingprocess for the passivation material layer may be a dry etching processsuch as a reactive ion etching (RIE) or another suitable etching processwhich is selected for the passivation material layer.

Thereafter, the first barrier film 122 and the second barrier film 124are sequentially deposited in the opening 129 and on the surface of thepassivation layer 127, as shown in FIG. 5B in accordance with someembodiments. In some embodiments, the first barrier film 122 is a metalnitride film such as TaN film, TiN film or another suitable metalnitride film with metal barrier ability. The first barrier film 122 isformed using a first deposition process with a first level of power. Thefirst deposition process includes a physical vapor deposition (PVD)process, sputtering, evaporation, atomic layer deposition (ALD) processor another suitable deposition process. In some embodiments, the firstlevel of power used in a PVD process is in a range from about 2000 W toabout 10000 W, for example about 6000 W. In some examples, the firstbarrier film 122 has a thickness in a range from about 400 Å to about800 Å, for example from about 484 Å to about 684 Å.

In some embodiments, the second barrier film 124 is a metal nitride filmsuch as TaN film, TiN film or another suitable metal nitride film withmetal barrier ability. The second barrier film 124 may be made of thesame material as that of the first barrier film 122. The second barrierfilm 124 is conformally formed on the first barrier film 122 using asecond deposition process with a second level of power that is lowerthan the first level of power. The second deposition process includes aPVD process, sputtering, evaporation, ALD process or another suitabledeposition process. In some embodiments, the second level of power usedin a PVD process is in a range from about 100 W to about 2000 W, forexample about 500 W. In some embodiments, the second barrier film 124has a thickness that is lesser than the thickness of the first barrierfilm 122. In some examples, the second barrier film 124 has a thicknessin a range from about 5 Å to about 200 Å, for example from about 10 Å toabout 180 Å.

According to the embodiments of the disclosure, the second barrier film124, which is formed using a low level of power deposition process, hasa higher nitrogen (N) atomic percentage than that of the first barrierfilm 122. In some embodiments, both the second barrier film 124 and thefirst barrier film 122 are TaN films. The second barrier film 124 has anatomic ratio of N to TaN in a range from about 0.86 to about 0.93. Thefirst barrier film 122 has an atomic ratio of N to TaN in a range fromabout 0.19 to about 0.31. In some embodiments, the N to TaN atomic ratioof the second barrier film 124 to the N to TaN atomic ratio of the firstbarrier film 122 is in a range from about 2.5 to about 5.0, for exampleabout 2.77 to about 4.90.

Thereafter, the aluminum-containing layer 126 is conformally formed onthe second barrier film 124, as shown in FIG. 5C in accordance with someembodiments. In some embodiments, the aluminum-containing layer 126 maybe an AlCu layer, an Al layer or other conductive material containingaluminum and providing a satisfactory conductivity. Thealuminum-containing layer 126 may be formed using a PVD process,sputtering, evaporation, ALD process or another suitable depositionprocess. In some embodiments, the aluminum-containing layer 126 has athickness that is greater than the thickness of the first barrier film122. In some examples, the aluminum-containing layer 126 has a thicknessin a range from about 500 Å to about 1000 Å.

Next, an etching mask 128 is formed on the aluminum-containing layer126, as shown in FIG. 5D in accordance with some embodiments. Theetching mask 128 may be a patterned photoresist, a hard mask or anothersuitable mask for use in etching processes of the aluminum-containinglayer 126, the second barrier film 124 and the first barrier film 122.The materials and the processes of forming the etching mask 128 may bethe same as or similar to those as described with respect to FIG. 3D,and not repeated again.

Thereafter, the aluminum-containing layer 126, the second barrier film124 and the first barrier film 122 are patterned using an etchingprocess to form the conductive pad structure 120, as shown in FIG. 5E inaccordance with some embodiments. The etching process may be dry etchingprocess such a RIE process or another suitable etching process. Theconductive pad structure 120 is formed in the opening 129 (as shown inFIG. 5A) and on the surface of the passivation layer 127. The conductivepad structure 120 may have a recess on the surface.

According to the embodiments of the disclosure, the second barrier film124 is made of metal nitride, for example TaN, and is formed using adeposition process with a lower level of power than that for the firstbarrier film 122. Therefore, the second barrier film 124 has a higher Natomic percentage than that of the first barrier film 122 and is formedwith an amorphous structure. As a result, the second barrier film 124can provide a better metal barrier ability to prevent the metal such asCu of the underlying top metal layer 106T from extrusion.

Moreover, the second barrier film 124 also has a higher compressivestress than that of the first barrier film 122. Therefore, the highercompressive stress of the second barrier film 124 can balance with thetensile stress of the aluminum-containing layer 126 to prevent the metalAl of the aluminum-containing layer 126 from extrusion. As a result, theconductive pad structure 120 of the embodiments can effectively avoidmetal extrusion such as Cu extrusion of the top metal layer 106T and themetal extrusion such as Al extrusion of the aluminum-containing layer126. The conductive pad structure 120 with a better quality is therebyachieved.

Next, another passivation layer 132 is formed on the conductive padstructure 120, as shown in FIG. 5F in accordance with some embodiments.The passivation layer 132 has an opening 133 to expose a portion of theconductive pad structure 120, for example a partial top surface of thealuminum-containing layer 126, for electrically coupling to an externalcircuit (not shown). The material and the process for forming thepassivation layer 132 may be the same as or similar to those of formingthe passivation layer 127, and not repeated again.

Thereafter, a conductive connection feature 134 is formed in the opening133 of the passivation layer 132 and is in contact with the conductivepad structure 120, as shown in FIG. 5G in accordance with someembodiments. The conductive connection feature 134 may be a conductivebump or pillar as shown in FIG. 5G, or a solder ball or a bonding wire(not shown). The conductive pad structure 120 is electrically coupled toan external circuit through the conductive connection feature 134 fortransferring electrical signals between the external circuit and thesemiconductor device with the conductive pad structure 120. Theconductive connection feature 134 may made of aluminum, copper, gold,silver, alloy thereof, a combination thereof, or another suitableconductive material. The conductive connection feature 134 may be formedusing evaporation, sputtering, electroplating or printing process.

FIG. 6 shows a cross-sectional view of a semiconductor device 400 havinga conductive pad structure 120, in accordance with some embodiments. Thedifference between the semiconductor device 400 of FIG. 6 and thesemiconductor device 100 of FIG. 1 is that a passivation layer 132 isformed on an interconnect structure 110 and on the conductive padstructure 120. The passivation layer 132 has an opening to expose apartial top surface of the conductive pad structure 120 for electricallycoupling to an external circuit (not shown). The passivation layer 132covers the sidewalls of the conductive pad structure 120 for protectingthe conductive pad structure 120 in subsequent fabrication.

The semiconductor device 400 includes a substrate 102 having multipleelectronic elements 104 formed therein or thereon, although onecomponent 104 is shown in FIG. 6, any number of the electronic elements104 can be formed in or on the substrate 102. The substrate 102 and theelectronic element 104 may be the same as or similar to those describedwith respect to FIG. 1 and not repeated again. The semiconductor device400 also includes the interconnect structure 110 formed on the substrate102 for electrically coupling various electronic elements 104 tofabricate integrated circuit. The interconnect structure 110 includesmultiple metal layers 106, a top metal layer 106T, and multiple vias 108in inter-metal dielectric (IMD) layers 107. The vias 108 providevertical connection for electrically coupling the adjacent metal layers106, and the top metal layer 106T. The materials and processes forforming the metal layers 106, the top metal layer 106T, the vias 108,and the IMD layers 107 may be the same as or similar to those describedwith respect to FIG. 1, and not repeated again.

In some embodiments, the conductive pad structure 120 including thefirst barrier film 122, the second barrier film 124 and thealuminum-containing layer 126 is formed on the top metal layer 106T ofthe interconnect structure 110. The materials and the processes forforming the first barrier film 122, the second barrier film 124 and thealuminum-containing layer 126 may be the same as or similar to thosedescribed with respect to FIG. 1, and not repeated again. According tothe embodiments of the disclosure, the conductive pad structure 120 caneffectively avoid metal extrusion such as Cu extrusion of the top metallayer 106T and the metal extrusion such as Al extrusion of thealuminum-containing layer 126. The conductive pad structure 120 with asatisfactory quality is thereby obtained.

Thereafter, the passivation layer 132 is formed on the interconnectstructure 110 and covering the sidewalls and a partial top surface ofthe conductive pad structure 120. The passivation layer 132 is patternedto have an opening to expose a portion of the conductive pad structure120. In some examples, the material of the passivation layer 132 may bepolyimide, epoxy resin or other organic insulating material, which arephotosensitive materials. The passivation material layer may be formedon the interconnect structure 110 and on the conductive pad structure120 using a coating process, and then the passivation material layer isexposed to light through a photomask. The passivation material layer ispatterned to form the passivation layer 132 using a development processto remove the exposed or unexposed portion of the photosensitivematerial. The passivation layer 132 has an opening to expose theconductive pad structure 120. The exposed or unexposed portion of thephotosensitive material is removed by the development process dependingon that the photosensitive material is positive or negative typephotoresist.

In some other examples, the material of the passivation layer 132 may besilicon oxide, silicon nitride, silicon oxynitride or other low-kdielectric material. The passivation layer 132 is patterned usingphotolithography and etching processes such as the above-mentioneddescription of the passivation layer 132 with respect to FIG. 5F.

Thereafter, a conductive connection feature 130 is formed in the openingof the passivation layer 132 and is in contact with the conductive padstructure 120, as shown in FIG. 6 in accordance with some embodiments.The conductive connection feature 130 may be a solder ball 138 with aunder bump metallurgy (UBM) layer 136 thereunder as shown in FIG. 6 inaccordance with some embodiments. In other examples, the conductiveconnection feature 130 may be a metal pillar, a metal bump or a bondingwire. The conductive pad structure 120 is electrically coupled to anexternal circuit through the conductive connection feature 130. Thesolder ball 138 may made of PbSn alloy or any suitable solder material,and the UBM layer 136 may made of multiple layers which may be selectedfrom a group consisting of Ti, Cr, TiW, Ni, Cu and Au. The conductiveconnection feature 130 may be formed using evaporation, sputtering,electroplating or printing process.

FIG. 7 shows a cross-sectional view of a semiconductor image sensordevice, for example a back side illumination (BSI) image sensor device500 having a conductive pad structure 120, in accordance with someembodiments. The BSI image sensor device 500 includes a substrate 102and multiple photo-sensing elements 104A, 104B and 104C formed in thesubstrate 102. The photo-sensing elements 104A, 104B and 104 may bephotodiodes, and each of the photo-sensing elements 104A, 104B and 104individually corresponds to one pixel of the BSI image sensor device500. Although there are three photo-sensing elements 104A, 104B and 104Cshown in FIG. 7, any number of the photo-sensing elements can be formedin the substrate 102 and are arranged into a pixel array of the BSIimage sensor device 500.

The substrate 102 may be a silicon wafer or other semiconductorsubstrate. The substrate 102 has a front side surface 102 f and a backside surface 102 b that is opposite to the front side surface 102 f. Insome embodiments, the conductive pad structure 120 is formed in thesubstrate 102 near the front side surface 102 f. According to theembodiments of the disclosure, the conductive pad structure 120 includesthe first barrier film 122, the second barrier film 124 and thealuminum-containing layer 126, which can be formed using the materialsand the processes the same as or similar to those described with respectto the conductive pad structure 120 of FIG. 1.

The BSI image sensor device 500 also includes the interconnect structure110 formed under the front side surface 102 f of the substrate 102, asshown in FIG. 7 in accordance with some embodiments. The interconnectstructure 110 is used for electrically coupling multiple transistors(not shown) in the substrate 102. The transistors are configured tocorrespond with each of the photo-sensing elements. The interconnectstructure 110 includes multiple metal layers 106, a top metal layer106T, and multiple vias 108 in inter-metal dielectric (IMD) layers 107.The materials and processes for forming the metal layers 106, the topmetal layer 106T, the vias 108, and the IMD layers 107 may be the sameas or similar to those described with respect to FIG. 1, and notrepeated again.

In addition, the first barrier film 122 of the conductive pad structure120 is in contact with the top metal layer 106T of the interconnectstructure 110. The aluminum-containing layer 126 of the conductive padstructure 120 is exposed through an opening 146 that is formed from theback side surface 102 b of the substrate 102 until to the surface of thealuminum-containing layer 126. According to the embodiments of thedisclosure, the conductive pad structure 120 can effectively avoid metalextrusion such as Cu extrusion of the top metal layer 106T and the metalextrusion such as Al extrusion of the aluminum-containing layer 126. Theconductive pad structure 120 with a satisfactory quality is therebyobtained.

Furthermore, a color filter layer 142 is formed on the back side surface102 b of the substrate 102, as shown in FIG. 7 in accordance with someembodiments. The color filter layer 142 includes multiple color filters,such as a red color filter 142A, a green color filter 142B, and a bluecolor filter 142C, which are disposed corresponding with each of thephoto-sensing elements, for example the photo-sensing elements 104A,104B and 104C, respectively.

In addition, a micro-lens layer 144 is disposed on the color filterlayer 142, as shown in FIG. 7 in accordance with some embodiments. Themicro-lens layer 144 includes multiple micro-lenses ML correspondingwith each of the color filters, for example the red color filter 142A,the green color filter 142B, and the blue color filter 142C,respectively. In the BSI image sensor device 500, a light 150illuminates on the back side surface 102 b of the substrate 102. Themicro-lenses ML can focus the light 150 on the correspondingphoto-sensing elements such as the photo-sensing elements 104A, 104B,and 104C in each pixel. Moreover, each of the various color filters142A, 142B and 142C can filter a certain color of light to thecorresponding photo-sensing elements 104A, 104B, and 104C, respectively.

Embodiments for fabricating semiconductor devices having a conductivepad structure with multi-barrier films are provided. The semiconductordevices may be various type semiconductor devices which include theconductive pad structures 120. The conductive pad structure 120 includesa first barrier film 122, a second barrier film 124 on the first barrierfilm 122, and an aluminum-containing layer 126 on the second barrierfilm 124. The conductive pad structure 120 is disposed on a top metallayer 106T of an interconnect structure 110. The top metal layer 106Tmay be made of Cu. The first barrier film 122 and the second barrierfilm 124 may be made of metal nitride, for example TaN. The firstbarrier film 122 is formed using a first deposition process with a firstlevel of power. The second barrier film 124 is formed using a seconddeposition process with a second level of power that is lower than thefirst level of power. As a result, the second barrier film 124 has ahigher N atomic percentage than that of the first barrier film 122, andthus the second barrier film 124 has an amorphous structure. Therefore,the second barrier film 124 can provide a better metal barrier abilityto prevent the metal such as Cu of the underlying top metal layer 106Tfrom extrusion.

In addition, the second barrier film 124 with the higher N atomicpercentage than that of the first barrier film 122 also has a highercompressive stress than that of the first barrier film 122. Therefore,the higher compressive stress of the second barrier film 124 can balancewith the tensile stress of the aluminum-containing layer 126 to preventthe metal Al of the aluminum-containing layer 126 from extrusion.

Accordingly, the conductive pad structures 120 of the embodiments of thedisclosure can effectively avoid the metal extrusion such as Cuextrusion of the top metal layer 106T and the metal extrusion such as Alextrusion of the aluminum-containing layer 126. The conductive padstructures 120 with satisfactory quality are thereby obtained. The yieldand the reliability of the semiconductor devices with the conductive padstructures 120 are thereby enhanced.

In some embodiments, a method of fabricating a semiconductor device isprovided. The method includes providing a substrate and forming aninterconnect structure on the substrate. The interconnect structureincludes a top metal layer. The method also includes forming a firstbarrier film on the top metal layer using a first deposition processwith a first level of power, and forming a second barrier film on thefirst barrier film using a second deposition process with a second levelof power that is lower than the first level of power. The method furtherincludes forming an aluminum-containing layer on the second barrierfilm. In addition, the method includes patterning the first barrierfilm, the second barrier film and the aluminum-containing layer to forma conductive pad structure.

In some embodiments, a method of fabricating a semiconductor device isprovided. The method includes providing a substrate having aninterconnect structure formed thereon. The interconnect structureincludes a top metal layer. The method also includes forming apassivation layer on the interconnect structure, and forming an openingin the passivation layer to expose the top metal layer. The methodfurther includes depositing a first tantalum-nitride (TaN) film in theopening using a first deposition process with a first level of power,and depositing a second tantalum-nitride (TaN) film on the first TaNfilm using a second deposition process with a second level of power thatis lower than the first level of power. In addition, the method includesdepositing an aluminum-containing layer on the second TaN film, andpatterning the aluminum-containing layer, the second TaN film and thefirst TaN film to form a conductive pad structure in the opening to bein contact with the top metal layer.

In some embodiments, a semiconductor device is provided. Thesemiconductor device includes a substrate having a plurality ofelectronic elements. The semiconductor device also includes aninterconnect structure over the substrate. The interconnect structureincludes a top metal layer. The semiconductor device further includes aconductive pad structure over the interconnect structure. In addition,the conductive pad structure includes a first barrier film on the topmetal layer. The conductive pad structure also includes a second barrierfilm on the first barrier film. The conductive pad structure furtherincludes an aluminum-containing layer on the second barrier film. Inaddition, both the first barrier film and the second barrier filminclude tantalum-nitride (TaN), and the second barrier film has anitrogen (N) atomic percentage that is higher than a nitrogen (N) atomicpercentage of the first barrier film.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method of fabricating a semiconductor device,comprising: forming an interconnect structure on a substrate, whereinthe interconnect structure comprises a top metal layer; forming a firstbarrier film on the top metal layer using a first deposition processwith a first level of power; forming a second barrier film on the firstbarrier film using a second deposition process with a second level ofpower that is lower than the first level of power; forming analuminum-containing layer on the second barrier film; and patterning thefirst barrier film, the second barrier film and the aluminum-containinglayer to form a conductive pad structure, wherein the first barrier filmand the second barrier film are made of metal nitride, and the secondbarrier film has a nitrogen (N) atomic percentage that is higher thanthe nitrogen (N) atomic percentage of the first barrier film.
 2. Themethod as claimed in claim 1, wherein the first level of power is in arange from about 2000 W to about 10000 W.
 3. The method as claimed inclaim 1, wherein the second level of power is in a range from about 100W to lower than about 2000 W.
 4. The method as claimed in claim 1,wherein both the first barrier film and the second barrier film are madeof tantalum-nitride (TaN).
 5. The method as claimed in claim 4, whereinthe second barrier film has an atomic ratio of N to TaN that is in arange from about 2.5 times to about 5 times greater than the atomicratio of N to TaN of the first barrier film.
 6. The method as claimed inclaim 4, wherein the first barrier film has an atomic ratio of N to TaNin a range from about 0.19 to about 0.31.
 7. The method as claimed inclaim 4, wherein the second barrier film has an atomic ratio of N to TaNin a range from about 0.86 to about 0.93.
 8. The method as claimed inclaim 1, wherein the second barrier film has a thickness that is lessthan the thickness of the first barrier film.
 9. The method as claimedin claim 1, wherein the top metal layer is made of copper (Cu), and thealuminum-containing layer is made of aluminum-copper (AlCu) alloy.
 10. Amethod of fabricating a semiconductor device, comprising: forming aninterconnect structure over a substrate, wherein the interconnectstructure comprises a top metal layer; forming a passivation layer onthe interconnect structure; forming an opening in the passivation layerto expose the top metal layer; depositing a first tantalum-nitride (TaN)film in the opening using a first deposition process with a first levelof power; depositing a second tantalum-nitride (TaN) film on the firstTaN film using a second deposition process with a second level of powerthat is lower than the first level of power; depositing analuminum-containing layer on the second TaN film; and patterning thealuminum-containing layer, the second TaN film and the first TaN film toform a conductive pad structure in the opening and in contact with thetop metal layer.
 11. The method as claimed in claim 10, wherein the topmetal layer is made of copper (Cu), and the aluminum-containing layer ismade of an aluminum-copper (AlCu) alloy.
 12. The method as claimed inclaim 10, wherein the second TaN film has a nitrogen (N) atomicpercentage that is higher than the nitrogen (N) atomic percentage of thefirst TaN film.
 13. The method as claimed in claim 10, wherein the firstlevel of power is in a range from about 2000 W to about 10000 W.
 14. Themethod as claimed in claim 13, wherein the second level of power is in arange from about 100 W to lower than about 2000 W.
 15. The method asclaimed in claim 10, wherein the first TaN film has a thickness in arange from about 2.5 times to about 70 times greater than a thickness ofthe second TaN film.
 16. The method as claimed in claim 10, wherein thefirst TaN film has a first N to TaN atomic ratio, the second TaN filmhas a second N to TaN atomic ratio, and a ratio of the second N to TaNatomic ratio to the first N to TaN atomic ratio is in a range from about2.5 to about
 5. 17. A method of fabricating a semiconductor device,comprising: forming an interconnect structure over a substrate, whereinthe interconnect structure comprises a top metal layer; and forming aconductive pad structure over the interconnect structure, comprising:depositing a first barrier film over the top metal layer; depositing asecond barrier film over the first barrier film; and depositing analuminum-containing layer over the second barrier film, wherein thefirst barrier film is made of a first material having a first nitrogen(N) atomic percentage and the second barrier film is made of a secondmaterial having a second nitrogen (N) atomic percentage, and the secondbarrier film has a higher compressive stress than that of the firstbarrier film.
 18. The method as claimed in claim 17, wherein the secondbarrier film has a thickness that is less than the thickness of thefirst barrier film.
 19. The method as claimed in claim 17, wherein thesecond N atomic percentage of the second barrier film is in a range fromabout 2.5 times to about 5 times greater than the first N atomicpercentage of the first barrier film.
 20. The method as claimed in claim17, wherein the first barrier film is deposited using a first depositionprocess with a first level of power, and the second barrier film isdeposited using a second deposition process with a second level of powerthat is lower than the first level of power.